Process of making waterproof paper



Patented Aug. 6, 1929.

UNITED STATS LESTER KIRSCHBRAUN,

i TENT OFFICE.

OF EVANSTON, ILLINOIS.

PROCESS OF MAKING WATERPROOF PAPER.

No Drawing. Application filed September This invention relates to improvements in waterproof paper and process of making same and has among its salient objects to provide a construction which is waterproof ed and more or less saturated simultaneously with the felting of the fibers in the formation of the sheet; to provide a product of the above character which is particularly characterized by bulking of the fibrous constituents, or in other words, the production of larger quantities or areas of paper from a given amount of fiber than is possible in the formation of ordinary paper; to provide a product in which the characteristics last referred to are primarily obtained through the introduction of a lrtu ninous or other water r op f loilrglpr, the latter thwartin not on y as a waterproofing and saturating agent, but also as a means for materially increasing the bulk or yield of the paper; to provide a product which can be formed in the well known paper machinery whether Fourdrinier, cylinder, wet board or combination of them; to provide a product in which the fibres while still interlaced are nevertheless loosely felted and extended more or less by the plastic waterproofing binder, thus producing a flexible, resilient sheet of relatively soft texture; this last characteristic permitting the use of harder, tougher and stiffer fibres than would otherwise be feasible in producing a product of the desired characteristics; to provide a novel process of forming the above product in which the waterproofing agent is in the form of a non-adhesive matrix.

Before describing the manner of carrying out my process, attention may be called to the following features. I can use various kinds of fibre such for example, old newspapers, rags, sulphate, sulphite and mechanical wood, mixed if desired with sawdust. The waterproofing agent is preferably a bitumen, solid or semi-solid at atmospheric temperature, such as asphalt, natural or artificial, coal tar pitches or analogous waterproofing binders. To carry out the process, this binder which is naturally sticky and ad hesive, is converted to a non-adhesive matrix. This matrix is mixed with the fibrous stock or pulp in a water vehicle before passing over the paper machine. When the mixture passes over the paper machine, the fibres interlace and interlock to form a felted sheet of whatever caliper is desired. This sheet, however, differs from ordinary paper in that 10, 1919. Serial No. 322,991.

the interstices between the fibres are larger than is ordinarily the case.

In other words, the fibres do not so closely interlock or lay up against each other. This spreading or bulking of the fibres is appar ently due to the interposition of the finely divided particles of bituminous binder. It is to be understood, however, that this bulking does not interfere with the formation of a perfect sheet For example, if the bitumen be extracted after the sheet is formed by means of suitable solvents such as benzol, a perfect sheet of paper remains. Nevertheless, it has been determined in actual practice that a much increased square yardage or area of paper is produced from a given quan tity of stock by this process than is possible in the ordinary manufacture of paper. For example, the weight of ordinary flooring or roofing felt produced in the usual way'is substantially equal to its caliper. That is, a 45 caliper sheet weighs approximately 45. If a sheet of this character be saturated with asphalt by immersion in the well known manner of producing saturated felt and if the absorption or saturation be 100%, of asphalt, the 45 caliper sheet will weigh approximately 90. A square foot sheet produced by my process, however, from substantially the same materials of the same caliper and with the same amount of asphalt in the form of my non-adhesive matrix will weigh about 62 on a paper makers scale. It is therefore apparent that a substantial bulking takes place.

I have found in certain instances that over more area of waterproof sheet is produced by this process than when the same sheet is formed in the usual way and saturated thereafter.

In carrylngout my process, I first make an aqueous mlxture or paste of water and an emulsifying agent such as colloidal clay. While this is hot, I add to it and thoroughly incorporate the waterproof adhesive binder, solid or semi-solid, such as asphalt, while the latter is in a hot liquid condition. I thus form a non-adhesive matrix which is in effect an emulsion; the asphalt being in the internal phase and the water and clay in the external phase. It is desirable that the degree of dispersion of the asphalt in the continuous phase be as fine as possible and I have ascertained that practically all of the dispersed asphalt will pass a wire mesh sieve, having 40,000 openings per square inch. It will, be understood, however, that much of that passing through such openings will be much. finer than the size of the openings described, certain particles approaching colloidal dimensions in size. This matrix is thinned and cooled with ater. It is then thoroughly mixed with the fibrous stock in the heater or mixing box. The mixture thus formed is thinned to the usual consistency of paper stock as it is fed to the machine.

As this mixture passes over the paper forming machine, the fibres are felted and a sheet of paper provided. w'th the bulking heretofore described. The water is removed and the sheet )ut over driers and dried in the usual way. The binder thereupon becomes adhesive and coalesces and unites with the fibres to form a waterproof sheet.

The following formula may be used, To 30 parts of dry weight of paper stock such as old newspaper, is added a matrix composed of 60 parts of binder emulsified with U) parts by weight of clay. This produces a sheet which is substantially fully saturated and entirely waterproof.

In some cases, it may be desirable to have less than complete saturation, as for example, in flooring felts to which a printed colored facing of paint is to be applied. This is desirable for the reason that the black asphalthas a tendency to become dissolved into the paint and work up through the paint, thereby causing discoloration of the facing design. \l here the sheet is not com pletely saturated, there is a tendency for the colored facing to work down into the sheet rather than for the asphalt to work up. The result is that with less than complete saturation, fewer coats of paint can be used and a more permanent design with cleaner colors maintained. In forming a sheet with less than complete saturation, the process is carried out exactly as before described in the case of complete saturation, except that a lesser quantity of as phalt is used in relation to the fibre. The following formula may be used for prod nets of this kind.

To 45 parts by weight of dry stock is added a matrix composed of 45 parts by weight of asphalt emulsified with 10 parts by weight of clay. It is to be understood, however, that even though a lesser amount of asphalt is used that the binder is nevertheless evenly distributed throughout the finished sheet, forming continuous films over the fibres.

I claim as my invention:

1. A process of forming waterproof paper, consisting in forming a non-adhesive matrix contained in an aqueous vehicle, and having a waterproof adhesive pitchy hinder, the particles of binder being dispersed and sutfieiently small that they will pass through a wire mesh having 40,000 openings per square inch, mixing the above matrix with fibrous pulp and then forming the same into sheets and drying out the aqueous vehicle.

2. A process of forming waterproof paper, consisting in forming a non-adhesive matrix contained in an aqueous vehicle and having an argilliferous emulsifying agent and a waterproof adhesive pitchy binder, the particles of binder being dispersed and sulliciently small that they will pass through a screen having 0,000 openings per square inch, mixing the matrix with fibrous pulp, forming same into sheets and drying out the aqueous vehicle.

LESTER KIRSCHBRAUN. 

